The invention relates to a drive assembly for motor vehicles having a front power unit which is elastically supported at the vehicle body and which is rigidly connected with a rear drive unit by means of a center tube through which the drive shaft extends.
In a known drive assembly of this general type (DE-PS 28 43 917), the center tube is rigidly connected with the power unit on one side and with the rear drive unit on its other side. This rear drive unit is formed by a gear change box in the case of a transaxle construction. This type of rigid drive assembly vibrates in response to gas force excitations of the engine during a load operation as a result of a torsional resonance of the transmission line. Here the center tube acts as a torsion spring and the transmission acts as the torsional mass.
The invention is based on an object of providing a drive assembly for motor vehicles having a front power unit which is elastically supported at the vehicle body and which is rigidly connected with a rear drive unit by means of a center tube through which the drive shaft extends in which, despite a rigid connection of the center tube with the power unit and the rear drive unit, a lowering of torsional resonances and therefore vibrations can be extensively achieved.
According to the invention, this is achieved by having the center tube have at least one axially limited longitudinal slot in the front area of low bending stress which connects to the power unit.
It is also advantageous if the longitudinal slot is arranged in a vertical longitudinal center plane of the center tube and in a wall area of the center tube which faces away from the vehicle bottom. Alternatively, or additionally, a longitudinal slot can be arranged in a wall area of the center tube that faces the vehicle bottom. An end of the longitudinal slot is arranged to start at a distance spaced from a front fastening flange of the center tube, which flange connects the tube to the power unit. The longitudinal slot is designed relatively narrow and has a length which extends approximately along a third of the overall length of the center tube.
It is also advantageous if the longitudinal slot has two ends that are designed as bores and if these ends are each partially covered by a tab which is fixedly connected with the center tube. Ideally the tab has a curved edge that extends in the direction of the longitudinal slot and with a center closer to the end of the tube.
It is also advantageous if the longitudinal slot is fixedly or partially closed off by an adhesive tape.
The torsional rigidity of this drive assembly is reduced by a center tube provided with at least one longitudinal slot situated in the area of low bending stress and which is rigidly connected with the units of the drive assembly. The bending rigidity of the center tube is substantially maintained unchanged as a result of the position of the longitudinal slot in a vertical longitudinal center plane of the tube and in the area of low bending stress. As a result, the torsional natural frequency of the drive assembly is reduced so that a torsional resonance of the transmission line in the driving rotational speed range will no longer occur.
By means of the special arrangement of the longitudinal slot in the center tube, the torsional resonance of the transmission line is shifted from the vehicle engine driving rotational speed range (1,400 rpm to 2,000 rpm) into a rotational speed range below 1,000 rpm and thus disturbing vibrational influences during driving ranges are therefore avoided.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.